Describe basic breathing mechanics.
- inspiratory muscles contract
- thoracic volume increases, thoracic pressure decreases
- air pushes in along pressure gradient
- expiration is passive
What is the difference between quiet versus forced breathing?
- diaphragm contracts for quiet breathing
- intercostal and accessory muscles are used for forced breathing
What is tidal volume?
- volume of air inspired during quiet breathing
- around 440ml
What is IRV?
- inspiratory reserve volume
- maximal inspiratory level
What is ERV?
- expiratory reserve volume
- resting expiratory level
What is RV?
- residual volume
- maximal expiratory volume
- some air always remain within the lungs
What is the dead space?
- also known as the conducting zone
- trachea, bronchi, terminal bronchiole
- not included in residual volume as no gas exchange occurs here
What is the respiratory zone?
- region of gas exchange
- respiratory bronchiole, alveolar duct, alveolar sac
What volume is the dead space?
150ml
What is the normal alveolar ventilation volume?
300ml
What is alveolar ventilation?
- volume of fresh air entering alveoli
- 150ml of air from dead space included from previous breath
Describe pulmonary gas exchange.
- occurs between alveolar air and pulmonary capillary blood
- gases move across wall by diffusion determined by the partial pressure gradient
Describe oxygen transport.
- 97% attached to haemoglobin
- 3% dissolved in plasma
How is CO2 transported in the blood?
- erythrocytes
- plasma
How is breathing controlled?
- breathing muscles are skeletal (voluntary)
- rhythm is generated from respiratory centres in brainstem and modified by sensory receptors
What causes hypoxic hypoxia?
- not enough oxygen reaching alveoli
- decreased oxygen diffusion into blood
What causes anaemic hypoxia?
Decreased oxygen transport in blood due to low haemoglobin
What causes stagnant hypoxia?
Decreased oxygen transport in blood due to low blood flow
What causes cytotoxic hypoxia?
Decreased oxygen utilisation by cells
What is cyanosis?
- blue colouration of skin or mucosa due to increased presence of deoxygenated blood
- can be central or peripheral
What causes central cyanosis?
Hypoxic hypoxia
What causes peripheral cyanosis?
Stagnant hypoxia
What are the four chambers of the heart?
- R atrium
- R ventricle
- L atrium
- L ventricle
What are the four valves of the heart?
- tricuspid
- pulmonary
- mitral (bicuspid)
- aortic
